The present invention relates to a poppet-type solenoid valve in which a large flow rate can be obtained with a small-sized solenoid valve and small power and particularly to a three-port poppet-type solenoid valve.
Because an attracting force acting on a movable core in energization is inversely proportional to the square of a stroke of the movable core in general in a solenoid used for a solenoid valve, it is effective to minimize the stroke of the movable core to obtain a large driving force with a small-sized solenoid and small power.
On the other hand, because an opening amount of a valve seat is substantially proportional to a stroke of a movable core in a poppet-type solenoid valve for opening and closing the valve seat by driving a poppet valve body by the movable core, it is necessary to maximize strokes of the movable core and the poppet valve body to control a large flow rate of fluid. However, if the stroke of the movable core is increased, an opening/closing stroke of the poppet valve body becomes large and the large flow rate of fluid can be controlled, but the attracting force of the movable core becomes small as described above. If the stroke of the movable core is reduced, the attracting force of the movable core can be increased, but the opening/closing stroke of the poppet valve body becomes small and the flow rate of fluid is reduced. Therefore, it is necessary to solve the above mutually contradictory problems to achieve the large flow rate with the small-sized solenoid and small power.
The present invention is intended to solve the above problems and it is a technical object of the invention to provide a poppet-type solenoid valve in which a valve seat is opened by as large an amount as possible to obtain a large flow rate while reducing a stroke of a movable core in a solenoid portion to obtain a large attracting force with the smallest possible solenoid and the smallest possible power.
It is a more concrete technical object of the invention to provide a solenoid valve in which a movable core drives a poppet valve body by a small stroke to open a supply valve seat and then the supply valve seat moves in such a direction as to further move away from the poppet valve body due to fluid pressure to increase a valve opening amount. When the movable core returns and the poppet valve body closes the supply valve seat, the supply valve seat moves due to fluid pressure to move the poppet valve body and the movable core to such positions as to open the valve by a small stroke.
To achieve the above objects, a solenoid valve of the present invention comprises: a housing including an input port, an output port, and a discharge port; a valve chamber which is formed in the housing, with which the input port and the discharge port respectively communicate through a supply valve seat and a discharge valve seat facing each other, and with which the output port communicates in a position between both the valve seats; a poppet valve body disposed in the valve chamber to open and close the supply valve seat and the discharge valve seat; and a solenoid portion including a movable core for causing the poppet valve body to carry out opening and closing operations.
The supply valve seat is formed on a valve seat body which is disposed for moving forward and rearward in such directions as to approach and move away from the discharge valve seat and which defines the valve chamber.
The valve seat body includes a supply flow path connecting the input port and the supply valve seat, first and second pressure receiving faces which have different pressure receiving areas and on which fluid pressure from the input port acts in opposite directions, and a third pressure receiving face on which fluid pressure in the valve chamber acts in the same direction as on the second pressure receiving face. The valve seat body moves forward in such a direction as to approach the discharge valve seat due to a fluid pressure operating force based on an area difference between the first and second pressure receiving faces when the supply valve seat is closed with the poppet valve body and moves rearward in such a direction as to move away from the discharge valve seat due to a fluid pressure operating force based on an area difference between the respective pressure receiving faces when the poppet valve body opens the supply valve seat.
In the solenoid valve having the above structure, when the solenoid portion is not energized, the poppet valve body closes the supply valve seat and opens the discharge valve seat. At this time, the fluid pressure from the input port acts on the first and second pressure receiving faces and the valve seat body moves forward in such a direction as to approach the discharge valve seat due to an operating force based on an area difference between the first and second pressure receiving faces. The poppet valve body and the movable core are pushed by the valve seat body and move to occupy such positions as to open the discharge valve seat by a small stroke.
If the solenoid portion is energized in this state, the poppet valve body opens the supply valve seat and closes the discharge valve seat by operation of the movable core. Therefore, the pressure fluid flows into the valve chamber from the supply valve seat and acts on the third pressure receiving face of the valve seat body. As a result, the valve seat body moves rearward in such a direction as to move away from the discharge valve seat due to the operating force based on the area difference between the respective pressure receiving faces and a gap between the supply valve seat and the poppet valve body is widened to increase an opening amount of the supply valve seat.
If energization of the solenoid portion is cancelled, the movable core returns and the poppet valve body closes the supply valve seat, opens the discharge valve seat, and opens the output port and the valve chamber to the atmosphere. Because the poppet valve body moves to a position of the supply valve seat in a rear position at this time, the discharge port opens temporarily by a large amount. Then, if the fluid pressure in the valve chamber reduces, the valve seat body moves forward toward the discharge valve seat due to the fluid pressure operating force based on the area difference between the first pressure receiving face and the second pressure receiving face. Therefore, the poppet valve body and the movable core are pushed by the valve seat body and move to occupy such positions as to open the discharge valve seat by the small stroke.
According to the invention, because the poppet valve body can be switched by a small stroke of the movable core, it is possible to generate a large attracting force required for valve opening with a small-sized solenoid. Moreover, once the poppet valve body opens the supply valve seat, the valve seat body moves with the supply valve seat due to the fluid pressure to increase the opening mount. Therefore, it is possible to switch a large flow rate of fluid by a small stroke.
According to a concrete embodiment of the invention, the valve seat body has a large-diameter portion and a small-diameter portion, the supply valve seat is formed and the third pressure receiving face facing the valve chamber is formed at the large-diameter portion, a space portion also functioning as a part of the supply flow path is formed between the large-diameter portion and the small-diameter portion, the first pressure receiving face is formed on a face on a side of the large-diameter portion facing the space portion, and the second pressure receiving face is formed on a face on a side of the small-diameter portion facing the space portion.
The large-diameter portion of the valve seat body is fitted in an inner hole formed in the housing through a sealing member and the small-diameter portion of the valve seat body is fitted for sliding through a sealing member in a small-diameter sleeve mounted in the inner hole.
In the solenoid valve of the invention, it is possible to provide an assist spring for repulsing the valve seat body toward the discharge valve seat in an assisting manner.
According to an embodiment of the invention, a spring guide in contact with the poppet valve body is movably provided around the supply valve seat in the valve seat body and a poppet spring is provided between the spring guide and the valve seat body.
According to another embodiment of the invention, a poppet guide for guiding opening and closing of the poppet valve body by sliding in the valve chamber is mounted to the poppet valve body and a poppet spring is disposed between the poppet guide and the valve seat body.